An aquatic demon with a humanoid form and sleek, angular features, exhibiting a deep indigo skin tone, eyes gleaming with a menacing intelligence. Its sharp, bared teeth are emphasized by an open, snarling mouth. The creature's brow is furrowed in a perpetual expression of malevolence. It is submerged in an underwater realm, surrounded by the undulating shadows of the ocean deep. The scene is rendered in Unreal Engine 4, showcasing stunning cinematic lighting that highlights the demon's intimidating presence and the ethereal beauty of its aquatic environment.